This invention relates to acoustic logging of boreholes and, more particularly, to a method and apparatus for determining the characteristics of the material forming the walls of the boreholes by logging the amplitudes of acoustic energy reflections from the walls of the boreholes.
In U.S. Pat. Nos. 3,369,626; 3,718,204; and 3,728,672, there are disclosed methods of and apparatus for scanning the walls of a borehole with acoustic energy. A transmitter and a receiver of acoustic energy are rotated within the borehole. The transmitter is cyclically energized to provide a beam of acoustic energy pulses for scanning the walls of the borehole. Reflected acoustic pulses are received by the receiver between transmitted acoustic pulses and are converted to reflection signals for recording on an electron beam display device. A sweep signal is generated each time the acoustic energy beam is rotated through a 360.degree. scanning pattern. Such sweep signal is applied to the horizontal deflection plates of the display device to sweep an electron beam horizontally across the face of the display device. The reflection signals are applied to the Z-axis of the display device to intensity modulate the electron beam as the beam is swept across the face of the display device to provide a picture which is a function of the time or distance from the transmitter and receiver to the wall of the borehole and of the hardness of the borehole wall.
In both the above-described patents the combination of transducer rotation along with vertical movement of the logging tool along the length of the borehole results in a continuous spiral of the borehole wall being scanned. The resulting display is a picture of the characteristics of the material forming the walls of the borehole at different depth points.